Our overall objective is to identify key regulatory mechanisms or factors influencing rate of growth and development by using several animal models. The animal models proposed for this study represent extremes in the pattern of development and as such offer us the opportunity to determine the physiological importance of such blood-borne factors as growth hormone, prolactin, somatomedin, and fibroblast proliferating activity. Because growth and development are controlled by the genetic, endocrine, nutritional, and biochemical influences on an individual, there is an obvious need for a multidisciplinary approach to study this problem. The background of the co-investigators listed above qualify them for this research approach. We are specifically interested in the study of blood-borne anabolic factors, their influence on tissue growth and metabolism, and the physiological importance of the "secondary messengers" (somatomedin and fibroblast proliferating activity). We have labelled these factors as secondary messengers because preliminary reports indicate that they may be regulated by pituitary hormones. The first phase of this project is directed at determining normal diurnal variations in serum growth factors and subsequent use of diurnal patterns to assess hormonal status and its relationship to growth. The second phase emphasizes ontogeny of fetal growth factors and effects of endocrinectomy or dietary changes on postnatal hormone status. The final phase will involve removing the influence of key blood factors by use of antibodies and measuring subsequent animal growth.